1. Field of the Invention
This invention relates to a method of and apparatus for detecting the location of an event, in particular the presence of an impurity in a gaseous medium.
2. Description of the Prior Art
It is known, when a plurality of locations need to be protected against fire, to provide at each location a detector to detect smoke in the air. Each detector detects any smoke generated by a fire at the location which it protects. The disadvantage of this arrangement is that if, for example, sixteen rooms or machines need protecting against fire, then sixteen detectors are required, with the high cost that this entails.
Aspirating systems for detecting smoke or explosive or poisonous gas in air are known which enable the detectors to be remote from the locations to be protected. In such a known aspirating system, an air sampling smoke or gas detector monitors from several points along the length of a pipe, but is unable to distinguish between inlets to the pipe, so that, if a smoke or gas signal is generated by such a detector, then the particular location along its pipe must still be found. If unambiguous identification of the smoke or gas source is required, an air sampling pipe is taken to each possible source location. The sampled air is taken either to a dedicated detector or to a scanning valve arrangement, so that the pipe carrying the smoke or gas can be identified, and hence the source located; however, both the system with the dedicated detectors and the system with the scanning valve arrangement are relatively expensive. The scanning valve arrangement is a multiplexing arrangement. In some versions of this arrangement the pipe outlets enter a common chamber containing or communicating with a single detector and either a series of flap valves are provided at the respective outlets, or a rotary valve plate formed with a single port is provided at the outlets, as disclosed in, for example, GB-A-2243475. In another version disclosed in, for example, U.S. Pat. No. 3,765,842 the sampling pipes extend through respective controlled valves to a common duct leading to a pump downstream of which is the single detector. In all versions the sampling pipes remain continuously open until smoke or gas is sensed by the detector when all except one pipe are closed in turn until the pipe carrying the smoke or gas is identified.